"It's four years next week since I've been in this role, and it's a pretty tough role... we also announced in the last week or two our results from our revised forecast and we hit all those forecasts, so now is the right time to hand on to someone else," he said.

Mr Quigley will continue to serve as CEO until the board appoints his replacement.

Opposition communications spokesman Malcolm Turnbull has been highly critical of Mr Quigley's performance, and believes he has been pushed.

"We know the [NBN Co] chairman Siobhan McKenna has been trying to sack him for some time, and he's been protected by Stephen Conroy, she's had headhunters out to find replacements, so finally he's left," Mr Turnbull said.

Earlier Ms McKenna paid tribute to Mr Quigley's work.

"NBN Co has been fortunate to have Mike as chief executive over the past four years. His intellect, tenacity and knowledge of telecommunications products and network architecture have taken NBN Co from a policy vision to a successful operating entity," she said.

"In a project of this magnitude you're constantly having to make judgements and make calls, and you invariably make mistakes along the way, but what I'm pleased about is we've made the right decisions in some of the big decisions," he said.

"I think that criticism, we have to take on board, and we have to keep questioning ourselves. And I think that’s why I think the scrutiny that we do see from our critics is something that's important."

Mr Quigley came out of retirement to become NBN Co's founding chief executive.

"My job was to lay the foundations for the NBN for the next 30 years. That job is largely complete," he said.

"The role of the next CEO will be to build on these foundations.

"The ramp-up in construction and the news last week that the company had passed more than 200,000 premises with fibre gives me further confidence that the NBN build can be delivered by 2021 in line with the projections in the company’s corporate plan."

Albanese, Wong issue their thanks

The Federal Government has thanked Mr Quigley for his role in establishing NBN Co.

Communications Minister Anthony Albanese and Finance Minister Penny Wong released a joint statement saying Mr Quigley was "eager to join the project because he understood the importance of nation-building infrastructure that is essential for our nation's economic future".